Trying to find buffering deadlock

primary.py

@@ -138,6 +138,7 @@ class Server:
                 arcname = path.decode('utf8', errors='surrogateescape')
                 try:
                     full_path = os.path.join(cwd, arcname)
+                    print('Add:', arcname, full_path, file=sys.stderr)
                     writer.add(full_path, arcname=arcname)
                 except FileNotFoundError:
                     self.log.MESSAGE("File disappeared '%s'" % full_path)